To be able to detect fires as early and reliably as possible, gas sensors are needed as fire detectors, which are able to detect fire gases in the smallest concentrations. A fire detector is described, e.g., in published German patent document DE 199 56 303, the measuring principle of which detector is based on a field-effect transistor (FET), whose gate electrode has at least one gas-sensitive coating such that the channel conductivity of the field-effect transistor changes as a function of the concentration of one or several fire gases to be detected.
The fire detector described in published German patent document DE 199 56 303 may also include, in addition to a measuring function on the basis of a FET, a scattered light detector. For this purpose, a light source is provided, which usually emits light at a wavelength in the infrared or near-infrared range into a measuring chamber, which is in contact with the surrounding atmosphere. The measuring chamber furthermore contains a detector unit, which allows for a determination of particles possibly contained in the gas phase. However, such a construction having a light source, a detector and a measuring function in the form of a FET, each as separate components, is expensive.
An object of the present invention is to provide a gas sensor which allows for a reliable and early detection of fires, but which nevertheless has a simple construction.